A main area of use for such an electrode assembly is in water systems in which pure water or ultrapure water is to be sterilized and rendered free of algae, in particular. In this case, the water system may comprise pipelines, collection tanks, open baths etc.
Electrode assemblies of the type mentioned initially are used, in particular, to disinfect rainwater, to disinfect ultrapure water circuits in the semiconductor industry and pharmaceuticals industry, to remove organic pollutants in rinse water, to purify water for the food industry and cosmetics industry, and in all types of industrial cooling-water circuits in order to prevent the growth of algae or the growth of bacteria or, in the case of high levels of contamination, to reduce the latter.
Such an electrode assembly can be used to generate oxidizing agents which oxidize germs and thus destroy or inactivate them.
The electrochemical generation of oxidizing agents has the advantage that it is possible, in principle, to adapt to the respective application. A large amount of oxidizing agent is thus required when a water system has already been contaminated with algae or biologically affected and is intended to be purified and disinfected. In contrast, once this operation has been concluded, the water system can be permanently kept in the disinfected and purified state, for which only a small amount of oxidizing agent is required from time to time.
A varying amount of oxidizing agent is also required when a water system has a high organic load as a result of an accident. A similar situation applies to the operation of filling a tank, in which a high level of oxidizing agent production is initially required in order to effect initial disinfection, while only relatively small amounts of oxidizing agent are then sufficient to maintain the disinfected state.
In principle, electrochemical methods are suitable for satisfying the different demands imposed on the production of oxidizing agents since the production of oxidizing agents can be controlled by supplying current.
In order to treat liquids with a low conductivity, for example ultrapure water, it is necessary, on account of the high resistance of the water, to use high voltages in order to generate the current densities required for the production of the oxidizing agents. This problem is partly solved by using polymeric solid electrolytes which, preferably in the form of a membrane having a thickness of a few tenths of a millimeter to a few millimeters, bridge the gap between the electrodes on the basis of their ion conductivity and are suitable as an interlayer between the electrodes in order to avoid a short circuit. On account of the relatively good ion conductivity of the polymeric solid electrolyte, the electrical potential of one electrode is brought very close to the other electrode, a film of water which is thus exposed to high current densities being situated between the surface of the polymeric solid electrolyte and the directly adjacent electrode.
Such electrode assemblies have been implemented for decades in the same manner in principle using the design of a “Fischer cell”. In this case, a pressure-exerting device which is formed from a surrounding housing is used to press the flat electrodes flat against the membrane which is situated between the electrodes and comprises a polymeric solid electrolyte. A sufficient contact pressure is produced by screwing flat pressure plates of the housing, which must take place with a minimum torque.
On account of the high level of required stability of the pressure plates of the housing, the construction of such a cell is high and necessitates involved handling. In addition, adaptation to higher throughputs is problematic since the effective electrode area of the cell would have to be enlarged for this purpose or the flow of liquid would have to be divided up and passed through a plurality of cells.
The Fischer cells were originally constructed using lead oxide electrodes. In this case, the use of a lead oxide anode has the further disadvantage that the electrode decomposes in water if it is not held at a protective potential. The use of an electrode assembly having a lead oxide anode is therefore possible only during continuous operation, with the result that the option of using the corresponding cell only when required does not apply.
DE 100 25 167 A1, for example, discloses the practice of using an electrode through which a liquid can flow on account of numerous groove-shaped channels and which has a surface comprising a doped diamond layer. Such electrodes have likewise been arranged in a cell constructed like a Fischer cell (cf. DE 295 04 323 U1). The associated handling disadvantages have been accepted for decades by those skilled in the art as being unalterable.